Polyacene and Semiconductor Formulation

ABSTRACT

The invention relates to novel polyacene compounds, organic semiconducting formulations and layers comprising them, a process for preparing the formulation and layer and electronic devices, including organic field effect transistors (OFETs), comprising the same.

FIELD OF THE INVENTION

The invention relates to novel polyacene compounds, methods of theirsynthesis, organic semiconducting formulations and layers comprisingthem, a process for preparing the formulation and layer and electronicdevices, including organic field effect transistors (OFETs), comprisingthe same.

BACKGROUND AND PRIOR ART

In recent years, there has been development of organic semiconductingmaterials in order to produce more versatile, lower cost electronicdevices. Such materials find application in a wide range of devices orapparatus, including organic field effect transistors (OFETs), organiclight emitting diodes (OLEDs), photodetectors, photovoltaic (PV) cells,sensors, memory elements and logic circuits to name just a few. Theorganic semiconducting materials are typically present in the electronicdevice in the form of a thin layer, for example less than 1 micronthick.

Pentacene has shown promise as an organic semiconducting material.Pentacene has been described as requiring a highly crystalline structurein order to provide a molecular orientation which results in good chargemobility. Thus, in the prior art, thin films of pentacene have beenvapour deposited, due in part to the fact that pentacene is ratherinsoluble in common solvents. However, vapour deposition requiresexpensive and sophisticated equipment. In view of the latter problem,one approach has been to apply a solution containing a precursorpentacene and then chemically converting, for example by heat, theprecursor compound into pentacene. However, the latter method is alsocomplex and it is difficult to control in order to obtain the necessaryordered structure for good charge mobility.

Soluble pentacene compounds have recently been described in the priorart as organic semiconducting compounds, see for example US 2003/0116755A and U.S. Pat. No. 6,690,029. The use of pentacenes in FETs has beensuggested in WO 03/016599, in which a solution of a soluble pentacenewas deposited on a substrate and the solvent evaporated to form a thinfilm of the pentacene. However, soluble pentacenes have been describedin U.S. Pat. No. 6,690,029 and WO 03/016599 as still requiring a highlycrystalline structure in the thin film for acceptable charge mobility,especially when used in FETs, which means that the pentacenes must stillbe deposited in a controlled way. Thus, the prior art is careful not todilute the pentacene in any way, otherwise it would be expected todisrupt the crystalline structure of the pentacene and hence reducecharge mobility.

Improved charge mobility is one goal of new electronic devices. Anothergoal is improved stability, film uniformity and integrity of the organicsemiconductor layer. One way potentially to improve organicsemiconductor layer stability and integrity in devices would be toinclude the organic semiconducting component in an organic binder.However, whenever an organic semiconducting component is combined with abinder it is effectively “diluted” by the binder and a reduction ofcharge mobility is to be expected. Among other things, diluting anorganic semiconductor by mixing with binders disrupts the molecularorder in the semiconducting layer. Diluting an organic semiconductingcomponent in the channel of an OFET for example is particularlyproblematic as any disruption of the orbital overlap between moleculesin the immediate vicinity of the gate insulator (the first few molecularlayers) is expected to reduce mobility. Electrons or holes are thenforced to extend their path into the bulk of the organic semiconductor,which is undesirable. Certain organic semiconducting materials areexpected to be more susceptible than others to the effects of use in abinder. Since pentacenes have been taught as requiring highly orderedstructures for useful charge mobility, it has not previously beenconsidered desirable to include pentacenes with binders. In WO 03/030278it was attempted to use binders but there it was shown that a gradualreduction of FET mobility occurs when a (precursor) pentacene is mixedwith increasing amounts of binder, even with amounts of less than 5%binder.

Certain low polarity binder resins are described in WO 02/45184 for usewith organic semiconductors in FETs. However, a reduction in chargemobility is still expected when the semiconductor is diluted in thebinder.

WO 2005/055248 A2 relates to a semiconductor formulation comprising anorganic binder and a polyacene, but does not explicitly disclose thematerials claimed in the present invention.

One aim of the present invention is to reduce or overcome thedisadvantages in organic semiconducting layers as described above. Otheraims of the present invention are immediately evident to the expert fromthe following detailed description.

It was now found that these aims can be achieved by providingsemiconducting materials, formulations and methods as claimed in thepresent invention. Especially, it was found that, by providingunsymmetric polyacenes as claimed in the present invention, chargetransport and semiconducting materials with improved solubility, chargecarrier mobility and stability can be obtained. Furthermore it was foundthat, when these unsymmetric polyacenes are provided in a formulationtogether with an organic binder, improved semiconducting materials withgood processability are obtained which do still show a surprisingly highcharge carrier mobility.

SUMMARY OF THE INVENTION

The invention relates to compounds of formula I (polyacenes)

wherein

-   n is 0, 1, 2, 3, 4 or 5,-   R¹⁻¹² denote, in case of multiple occurrence independently of one    another, identical or different groups selected from H, halogen,    —CN, —NC, —NCO, —NCS, —OCN, —SCN, —C(═O)NR⁰R⁰⁰, —C(═O)X, —C(═O)R⁰,    —NH₂, —NR⁰R⁰⁰, —SH, —SR⁰, —SO₃H, —SO₂R⁰, —OH, —NO₂, —CF₃, —SF₅,    optionally substituted silyl, or carbyl or hydrocarbyl with 1 to 40    C atoms that is optionally substituted and optionally comprises one    or more hetero atoms,-    wherein at least two groups R¹⁻¹² that are present in the compound    are different from H,-   X is halogen,-   R⁰ and R⁰⁰ are independently of each other H or an optionally    substituted carbyl or hydrocarbyl group optionally comprising one or    more hetero atoms,-   optionally two or more of the substituents R¹⁻¹², which are located    on adjacent ring positions of the polyacene, constitute a further    saturated, unsaturated or aromatic ring system having 4 to 40 C    atoms, which is monocyclic or polycyclic, is fused to the polyacene,    is optionally intervened by one or more groups selected from —O—,    —S— and —N(R⁰)—, and is optionally substituted by one or more    identical or different groups R¹,-   optionally one or more of the carbon atoms in the polyacene skeleton    or in the rings formed by R¹⁻¹⁴ are replaced by a heteroatom    selected from N, P, As, O, S, Se and Te,    wherein the compounds do not have a symmetry axis or symmetry plane    perpendicular to their long molecular axis.

Especially preferred are compounds of formula I wherein

-   a) if n is 2, then R⁶ and R¹¹ are different from H, and/or-   b) if n is 1, then R¹, R⁴, R⁶ and R¹¹ are not identical groups and    R⁵, R⁷, R¹⁰ and R¹² are not identical groups, and/or-   c) if n is 1, then the groups R² and R³ and the groups R⁸ and R⁹ do    not at the same time form a thiophene ring with the polyacene,-   d) if n is 0, then R⁵ and R¹² are different from H, and/or-   e) if n is 2, then R² and R³ are different from COOCH₃.

The invention further relates to the use of compounds of formula I ascharge carrier materials and organic semiconductors.

The invention further relates to an organic semiconducting formulationcomprising one or more compounds of formula I, one or more organicbinders, or precursors thereof, preferably having a permittivity ∈ at1,000 Hz of 3.3 or less, and optionally one or more solvents.

The invention further relates to an organic semiconducting layercomprising a compound of formula I or an organic semiconductingformulation as described above and below.

The invention further relates to a process for preparing an organicsemiconducting layer as described above and below, comprising thefollowing steps

-   (i) depositing on a substrate a liquid layer of a formulation which    comprises one or more compounds of formula I, one or more organic    binders or precursors thereof, and optionally one or more solvents,-   (ii) forming from the liquid layer a solid layer which is the    organic semiconducting layer,-   (iii) optionally removing the layer from the substrate.

The invention further relates to the use of the compounds, formulationsand layers as described above and below in an electronic, optical orelectrooptical component or device.

The invention further relates to an electronic, optical orelectrooptical component or device comprising one or more compounds,formulations or layers as described above and below.

Said electronic, optical or electrooptical component or device includes,without limitation, an organic field effect transistor (OFET), thin filmtransistor (TFT), component of integrated circuitry (IC), radiofrequency identification (RFID) tag, organic light emitting diode(OLED), electroluminescent display, flat panel display, backlight,photodetector, sensor, logic circuit, memory element, capacitor,photovoltaic (PV) cell, charge injection layer, Schottky diode,planarising layer, antistatic film, conducting substrate or pattern,photoconductor, and electrophotographic element.

DETAILED DESCRIPTION OF THE INVENTION

The proviso in formula I should exclude polyacenes having symmetry axisperpendicular to their long molecular axis (wherein ‘long molecularaxis’ means the long axis of the polyacene core), like the followingcompound

(wherein the arrow indicates the direction of the long molecular axisand x denotes a rotational symmetry axis perpendicular to said longmolecular axis and perpendicular to the drawing plane), and polyacenesthat have a symmetry plane perpendicular to their long molecular axis,like the following compound

(wherein the arrow indicates the direction of the long molecular axisand the broken line denotes a mirror plane perpendicular to said longmolecular axis and perpendicular to the drawing plane).

However, the proviso in formula I does not exclude polyacenes that havea mirror plane parallel to their long molecular axis (meaning the longaxis of the polyacene core), like the following compounds

(wherein the broken line denotes a mirror plane perpendicular to thedrawing plane but parallel to the long molecular axis).

The non-symmetrical structure of the polyacenes of formula I leads toadvantageous properties. Thus, introducing asymmetry into the polyacenederivative affects its solid-state order. This provides a facile meansof tuning the material properties related to crystal packing. Thecrystal packing in turn determines the mobility, stability andsolubility of the material. When the polyacenes are used as chargetransport or semiconductor materials in electronic devices, these arekey properties relating for example to good processability during devicepreparation. Unless stated otherwise, groups like R¹, R² etc., orindices like n etc., in case of multiple occurrence are selectedindependently from each other, and may be identical or different fromeach other. Thus, several different groups might be represented by asingle label like for example “R¹”.

The terms ‘alkyl’, ‘aryl’ etc. also include multivalent species, forexample alkylene, arylene etc. The term ‘aryl’ or ‘arylene’ means anaromatic hydrocarbon group or a group derived from an aromatichydrocarbon group. The term ‘heteroaryl’ or ‘heteroarylene’ means an‘aryl’ or ‘arylene’ group comprising one or more hetero atoms.

The term ‘carbyl group’ as used above and below denotes any monovalentor multivalent organic radical moiety which comprises at least onecarbon atom either without any non-carbon atoms (like for example—C≡C—), or optionally combined with at least one non-carbon atom such asN, O, S, P, Si, Se, As, Te or Ge (for example carbonyl etc.). The terms‘hydrocarbon group’, and ‘hydrocarbyl group’ denote a carbyl group thatdoes additionally contain one or more H atoms and optionally containsone or more hetero atoms like for example N, O, S, P, Si, Se, As, Te orGe.

A carbyl or hydrocarbyl group comprising a chain of 3 or more C atomsmay also be linear, branched and/or cyclic, including spiro and/or fusedrings.

Preferred carbyl and hydrocarbyl groups include alkyl, alkoxy,alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy and alkoxycarbonyloxy,each of which is optionally substituted and has 1 to 40, preferably 1 to25, very preferably 1 to 18 C atoms, furthermore optionally substitutedaryl or aryloxy having 6 to 40, preferably 6 to 25 C atoms, furthermorealkylaryloxy, arylcarbonyl, aryloxycarbonyl, arylcarbonyloxy andaryloxycarbonyloxy, each of which is optionally substituted and has 6 to40, preferably 7 to 40, very preferably 7 to 25 C atoms.

The carbyl or hydrocarbyl group may be a saturated or unsaturatedacyclic group, or a saturated or unsaturated cyclic group. Unsaturatedacyclic or cyclic groups are preferred, especially alkenyl and alkynylgroups (especially ethynyl). Where the C₁-C₄₀ carbyl or hydrocarbylgroup is acyclic, the group may be linear or branched. The C₁-C₄₀ carbylor hydrocarbyl group includes for example: a C₁-C₄₀ alkyl group, aC₂-C₄₀ alkenyl group, a C₂-C₄₀ alkynyl group, a C₃-C₄₀ alkyl group, aC₄-C₄₀ alkyldienyl group, a C₄-C₄₀ polyenyl group, a C₆-C₁₈ aryl group,a C₆-C₄₀ alkylaryl group, a C₆-C₄₀ arylalkyl group, a C₄-C₄₀ cycloalkylgroup, a C₄-C₄₀ cycloalkenyl group, and the like. Preferred among theforegoing groups are a C₁-C₂₀ alkyl group, a C₂-C₂₀ alkenyl group, aC₂-C₂₀ alkynyl group, a C₃-C₂₀ alkyl group, a C₄-C₂₀ alkyldienyl group,a C₆-C₁₂ aryl group and a C₄-C₂₀ polyenyl group, respectively; morepreferred are a C₁-C₁₀ alkyl group, a C₂-C₁₀ alkenyl group, a C₂-C₁₀alkynyl group (especially ethynyl), a C₃-C₁₀ alkyl group, a C₄-C₁₀alkyldienyl group, a C₆-C₁₂ aryl group and a C₄-C₁₀ polyenyl group,respectively; and most preferred is C₂₋₁₀ alkynyl.

Further preferred carbyl and hydrocarbyl groups include straight-chain,branched or cyclic alkyl with 1 to 40, preferably 1 to 25 C-atoms, whichis unsubstituted, mono- or polysubstituted by F, Cl, Br, I or CN, andwherein one or more non-adjacent CH₂ groups are optionally replaced, ineach case independently from one another, by —O—, —S—, —NH—, —NR⁰—,—SiR⁰R⁰⁰—, —CO—, —COO—, —OCO—, —O—CO—O—, —S—CO—, —CO—S—, —CO—NR⁰—,—NR⁰—CO—, —NR⁰—CO—NR⁰⁰—, —CX¹═CX²— or —C≡C— in such a manner that Oand/or S atoms are not linked directly to one another, with R⁰ and R⁰⁰having one of the meanings given as described above and below and X¹ andX² being independently of each other H, F, Cl or CN.

R⁰ and R⁰⁰ are preferably selected from H, straight-chain or branchedalkyl with 1 to 12 C atoms or aryl with 6 to 12 C atoms.

Halogen is F, Cl, Br or I.

Preferred alkyl and arylalkyl groups include, without limitation,methyl, ethyl, n-propyl, iso-propyl, n-butyl, t-butyl, dodecanyl,trifluoromethyl, perfluoro-n-butyl, 2,2,2-trifluoroethyl, benzyl,2-phenoxyethyl, etc. Preferred alkynyl groups include without limitationethynyl and propynyl.

Preferred aryl groups include, without limitation, phenyl, 2-tolyl,3-tolyl, 4-tolyl, naphthyl, biphenyl, 4-phenoxyphenyl, 4-fluorophenyl,3-carbomethoxyphenyl, 4-carbomethoxyphenyl, etc.

Preferred alkoxy groups include, without limitation, methoxy, ethoxy,2-methoxyethoxy, t-butoxy, etc.

Preferred aryloxy groups include, without limitation, phenoxy,naphthoxy, phenylphenoxy, 4-methylphenoxy, etc.

Preferred amino groups include, without limitation, dimethylamino,methylamino, methylphenylamino, phenylamino, etc.

If two or more of the substituents R¹-R¹² together with the polyaceneform a ring system, this is preferably a 5-, 6- or 7-membered aromaticor heteroaromatic ring, preferably selected from pyridine, pyrimidine,thiophene, selenophene, thiazole, thiadiazole, oxazole and oxadiazole,especially preferably thiophene or pyridine.

The optional substituents on the ring groups and on the carbyl andhydrocarbyl groups for R¹ etc. include, without limitation, silyl,sulpho, sulphonyl, formyl, amino, imino, nitrilo, mercapto, cyano,nitro, halogen, C₁₋₁₂alkyl, C₆₋₁₂ aryl, C₁₋₁₂ alkoxy, hydroxy and/orcombinations thereof. These optional groups may comprise all chemicallypossible combinations in the same group and/or a plurality (preferablytwo) of the aforementioned groups (for example amino and sulphonyl ifdirectly attached to each other represent a sulphamoyl radical).

Preferred substituents include, without limitation, F, Cl, Br, I, —CN,—NO₂, —NCO, —NCS, —OCN, —SCN, —C(═O)NR⁰R⁰⁰, —C(═O)X, —C(═O)R⁰, —NR⁰R⁰⁰,—OH, —SF₅, wherein R⁰, R⁰⁰ and X are as defined above, optionallysubstituted silyl, aryl with 1 to 12, preferably 1 to 6 C atoms, andstraight chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl,alkylcarbonlyoxy or alkoxycarbonyloxy with 1 to 12, preferably 1 to 6 Catoms, wherein one or more H atoms are optionally replaced by F or Cl.Examples for these preferred substituents are F, Cl, CH₃, C₂H₅, C(CH₃)₃,CH(CH₃)₂, CH₂CH(CH₃)C₂H₅OCH₃, OC₂H₅, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅,CF₃, OCF₃, OCHF₂ and OC₂F₅.

Very preferred optional substituents comprise optionally substitutedsilyl, amino, F, Cl, CH₃, C₂H₅, C(CH₃)₃, CH(CH₃)₂, CH₂CH(CH₃)C₂H₅.

The siiyi group is optionally substituted and is preferably selected ofthe formula —SiR′R″R′″. Therein, each of R′, R″ and R′″ are identical ordifferent groups selected from H, a C₁-C₄₀-alkyl group, preferablyC₁-C₄-alkyl, most preferably methyl, ethyl, n-propyl or isopropyl, aC₆-C₄₀-aryl group, preferably phenyl, a C₆-C₄₀-arylalkyl group, aC₁-C₄₀-alkoxy group, or a C₆-C₄₀-arylalkyloxy group, wherein all thesegroups are optionally substituted for example with one or more halogenatoms. Preferably, R′, R″ and R′″ are each independently selected fromoptionally substituted C₁₋₁₀-alkyl, more preferably C₁₋₄-alkyl, mostpreferably C₁₋₃-alkyl, for example isopropyl, and optionally substitutedC₆₋₁₀-aryl, preferably phenyl. Further preferred is a silyl group offormula —SiR′R″″ wherein R″″ forms a cyclic silylalkyl group togetherwith the Si atom, preferably having 1 to 8 C atoms.

In one preferred embodiment of the silyl group, R′, R″ and R′″ areidentical groups, for example identical, optionally substituted, alkylgroups, as in triisopropylsilyl. Very preferably the groups R′, R″ andR′″ are identical, optionally substituted C₁₋₁₀, more preferably C₁₋₄,most preferably C₁₋₃ alkyl groups. A preferred alkyl group in this caseis isopropyl.

A silyl group of formula —SiR′R″R′″ or —SiR′R″″ as described above is apreferred optional substituent for the C₁-C₄₀-carbyl or hydrocarbylgroup.

Preferred groups —SiR′R″R′″ include, without limitation, trimethylsilyl,triethylsilyl, tripropylsilyl, dimethylethylsilyl, diethylmethylsilyl,dimethylpropylsilyl, dimethylisopropylsilyl, dipropylmethylsilyl,diisopropylmethylsilyl, dipropylethylsilyl, diisopropylethylsilyl,diethylisopropylsilyl, triisopropylsilyl, trimethoxysilyl,triethoxysilyl, triphenylsilyl, diphenylisopropylsilyl,diisopropylphenylsilyl, diphenylethylsilyl, diethylphenylsilyl,diphenylmethylsilyl, triphenoxysilyl, dimethylmethoxysilyl,dimethylphenoxysilyl, methylmethoxyphenylsilyl, etc., wherein the alkyl,aryl or alkoxy group is optionally substituted.

In some cases it may be desirable to control the solubility of thesemiconducting compounds of formula I in common organic solvents inorder to make devices easier to fabricate. This may have advantages inmaking an FET for example, where solution coating, say, a dielectriconto the semiconducting layer may have a tendency to dissolve thesemiconductor. Also, once a device is formed, a less solublesemiconductor may have less tendency to “bleed” across organic layers.In one embodiment of a way to control solubility of the semiconductingcompounds of formula I above, the compounds comprise silyl groupsSiR′R″R′″ wherein at least one of R′, R″ and R′″ contains an optionallysubstituted aryl, preferably phenyl, group. Thus, at least one of R′, R″and R′″ may be an optionally substituted C₆₋₁₈ aryl, preferably phenyl,group, an optionally substituted C₆₋₁₈ aryloxy, preferably phenoxy,group, an optionally substituted C₆₋₂₀ arylalkyl, for example benzyl,group, or an optionally substituted C₆₋₂₀ arylalkyloxy, for examplebenzyloxy, group. In such cases, the remaining groups, if any, among R′,R″ and R′″ are preferably C₁₋₁₀, more preferably C₁₋₄, alkyl groupswhich are optionally substituted.

Especially preferred are the following compounds of formula I:

-   -   n is 0, 1 or 2,    -   n is 0 and R⁵ and R¹² are different from H,    -   n is 1 and the groups R⁵ and R¹² and/or the groups R⁶ and R¹¹        are different from H,    -   n is 2 and R⁶ and R¹¹ are different from H,    -   R² and R³ are different from H, and R⁸ and R⁹ are different from        R² and R³    -   R² and R³ are different from H, and R⁸ and R⁹ are H,    -   the groups R² and R³ and/or the groups R⁸ and R⁹ together with        the polyacene form a 5-, 6- or 7-membered aromatic or        heteroaromatic ring, preferably selected from pyridine,        pyrimidine, thiophene, selenophene, thiazole, thiadiazole,        oxazole and oxadiazole, especially preferably selected from the        following groups or their mirror images (wherein the asterisks        denote the positions where the respective group is fused to the        polyacene)

-   -    preferably together with n=0 and R⁵ and R¹² being different        from H,    -   the ring formed by R² and R³ and the ring formed by R⁸ and R⁹        are different from each other,    -   if R² and R³ form the ring

-   -    then R⁸ and R⁹ do not form the ring

-   -    especially in case n=1,    -   at least two of R¹⁻¹², in case n=0 or 1 preferably R⁵ and R¹²,        and in case n=2 preferably R⁶ and R¹¹, denote —C≡C-MR′R″R′″ or        —C≡C-MR′R″″, wherein M is Si or Ge and R′, R″, R′″ and R″″ are        as defined above,    -   the group —C≡C-MR′R″R′″ is —C≡C—SiR₃, wherein R is        straight-chain, branched or cyclic C₁₋₁₂-alkyl or C₁₋₁₂-alkoxy,        or optionally substituted monocyclic, polycyclic or fused aryl        having 5 to 12 C atoms.

Further preferred are the following compounds

wherein R¹⁻¹² are as defined in formula I and

-   A and B are independently of each other a saturated, unsaturated or    aromatic ring system having 4 to 40 C atoms, which is monocyclic or    polycyclic, is fused to the polyacene, is optionally intervened by    one or more groups selected from —O—, —S— and —N(R⁰)—, and is    optionally substituted by one or more identical or different groups    R¹.

Preferably A and B are a 5-, 6- or 7-membered aromatic or heteroaromaticring, preferably selected from pyridine, pyrimidine, thiophene,selenophene, thiazole, thiadiazole, oxazole and oxadiazole, especiallypreferably thiophene or pyridine.

Preferably A and B are different rings.

Very preferred are compounds of the following subformulae

wherein R^(1a), R^(2a), R^(3a), R^(4a), R^(8a) and R^(9a) have one ofthe meanings of R¹ as given above and below,R^(5a), R^(6a), R^(11a) and R^(12a) preferably denote —C≡C-MR′R″R′″ or—C≡C-MR′R″″ or —C≡C—SiR₃ as defined above and below,R^(13a) and R^(14a) preferably denote alkyl as defined above and below.

Examples of preferred compounds include, without limitation:

whereinR^(x), R^(y) and R^(z) are identical or different straight-chain orbranched alkyl or alkoxy with 1 to 12 C atoms that is optionallyfluorinated, or aryl, aryloxy or arylalkyl with 6 to 18 C atoms that isoptionally substituted,alkyl′ and alkyl″ are straight-chain or branched alkyl or alkoxy with 1to 12 C atoms that is optionally fluorinated,X′ and X″ are halogen, preferably F.SiR^(x)R^(y)R^(z) is preferably selected from trimethylsilyl,triethylsilyl, tripropylsilyl, dimethylethylsilyl, diethylmethylsilyl,dimethylpropylsilyl, dimethylisopropylsilyl, dipropylmethylsilyl,diisopropylmethylsilyl, dipropylethylsilyl, diisopropylethylsilyl,diethylisopropylsilyl, triisopropylsilyl, trimethoxysilyl,triethoxysilyl, triphenylsilyl, diphenylisopropylsilyl,diisopropylphenylsilyl, diphenylethylsilyl, diethylphenylsilyl,diphenylmethylsilyl, triphenoxysilyl, dimethylmethoxysilyl,dimethylphenoxysilyl or methylmethoxyphenylsilyl, wherein the alkyl,aryl or alkoxy group is optionally substituted.alkyl′ and alkyl″ are preferably selected from methyl, ethyl, n-propyl,isopropyl, n-butyl, t-butyl, dodecanyl, trifluoromethyl,perfluoro-n-butyl, 2,2,2-trifluoroethyl, benzyl, 2-phenoxyethyl, phenyl,2-tolyl, 3-tolyl, 4-tolyl, naphthyl, biphenyl, 4-phenoxyphenyl,4-fluorophenyl, 3-carbomethoxyphenyl, 4-carbomethoxyphenyl, methoxy,ethoxy, 2-methoxyethoxy, t-butoxy, phenoxy, naphthoxy, phenylphenoxy,4-methylphenoxy.

The compounds of the present invention can be synthesized according toor in analogy to known methods or to the methods described below.Further methods can be taken from the examples.

Certain polyacene compounds have been described in US 2003/0116755 A andU.S. Pat. No. 6,690,029 and the methods disclosed therein forsynthesizing polyacenes may be employed in the present invention inorder to make the polyacene compounds described herein. Methods formaking polyacenes are also described in U.S. Pat. No. 3,557,233.Alternatively, methods within the skill and knowledge of persons skilledin the art which may be used to synthesize polyacene compounds inaccordance with the present invention are disclosed in Organic Letters2004, Volume 6, number 10, pages 1609-1612.

Unsymmetric polyacenes have been reported, which are synthesized by ahomologation procedure from tetracene derivatives (see T. Takahashi, M.Kitamura, B. Shen, K. Nakajima, J. Am. Chem. Soc, 2000, 122,12876-12877).

The present invention also relates to a method of preparing polyacenesof formula I using a synthetic route based on an aldol condensationprocess.

Polyacenes derivatives are usually prepared from their correspondingacene quinones which are obtained from an aldol condensation ofphthalaldehydes with 1,4-cyclohexanedione. This aldol condensationaffords only symmetrical compounds.

The present invention uses this method and shows that the aldolcondensation can be achieved not only with the dione, but on itstautomeric form, the anthracene-1,4-diol in the example of the2,3-dihydroanthracene-1,4-dione. It is believed that this is due to thefact that in basic media, both isomers form same enolate anion reactingin the aldol condensation, as shown in scheme 1.

The invention thus further relates to a process of preparing anunsymmetrical polyacene, preferably selected of formula I, by reactingan anthracene-1,4-diol with an optionally substituted phthalaldehyde oran optionally substituted heteroaromatic dicarboxaldehyde in thepresence of a base.

Preferably the silylethynylated acene derivatives 5 and 7 are obtainedfrom their corresponding acene quinones 4 and 6 as shown in Scheme 2,according to published procedures (see C. D. Sheraw, T. N. Jackson, D.L. Eaton, J. E. Anthony, Adv. Mater, 2003, 23, 2009-2011).

The acene quinones 4 and 6 are both synthesised from an aldolcondensation of a phthalaldehyde, respectively the4,5-dimethylphthalaldehyde 3 (see O. Farooq, Synthesis, 1994, 1035-1037)and the 2,3-thiophenedicarboxaldehyde, with the 1,4-dihydroxyanthracene2 as shown in Scheme 3.

Compound 2 can be prepared from commercially available quinizarin asshown in Scheme 4, according to literature methods (see D. H. Hua, M.Tamura, X. Huang, H. A. Stephany, B. A. Helfrich, E. M. Perchellet, B.J. Sperfslage, J.-P. Perchellet, S. Jiang, D. E. Kyle, P. K. Chiang, J.Org. Chem, 2002, 2907-2912).

Surprisingly and beneficially, it has been found in accordance with thepresent invention that combining specified soluble polyacene compoundsof formula I (hereinafter also referred to as “the polyacene”),especially compounds of the preferred formulae as described above andbelow, with an organic binder resin (hereinafter also referred to as“the binder”) results in little or no reduction in charge mobility ofthe polyacene, even an increase in some instances. For instance, thesoluble polyacene may be dissolved in a binder resin (for examplepoly(α-methylstyrene) and deposited (for example by spin coating), toform an organic semiconducting layer yielding a high charge mobility, offor example 0.1-1.5 cm²V⁻¹ s⁻¹. This result is particularly unexpectedgiven that the prior art teaches that in order to achieve such highmobilities a polyacene compound is expected to require strong molecularordering. In FETs dilution in a binder would be expected to yield atleast an order of magnitude reduction in mobility. It has also now beenfound that surprisingly even at a 1:1 ratio of binder:polyacene themobility is comparable to that of a pure polyacene compound used alone.The results produced by the present invention are therefore surprisingfor both a) maintaining the mobility despite potential disruption ofmolecular order, and b) maintaining mobility despite the expectedincrease of intermolecular distance. At the same time, a semiconductinglayer formed therefrom exhibits excellent film forming characteristicsand is particularly stable.

Once an organic semiconducting layer formulation of high mobility isobtained by combining a polyacene with a binder, the resultingformulation leads to several other advantages. For example, since thepolyacenes are soluble they may be deposited in a liquid form, forexample from solution. With the additional use of the binder it has nowbeen found that the formulation may be coated onto a large area in ahighly uniform manner. Without the use of binders the polyacene cannotbe spin coated onto large areas as it does not result in uniform films.In the prior art, spin and dropcasting of a pure polyacene layer may insome cases result in relatively high mobility, however, it is difficultto provide a large area film with a constant mobility over the entiresubstrate which is a specific requirement for electronic devices.Furthermore, when a binder is used in the formulation it is possible tocontrol the properties of the formulation to adjust to printingprocesses, for example viscosity, solid content, surface tension. Whilstnot wishing to be bound by any particular theory it is also anticipatedthat the use of a binder in the formulation fills in volume betweencrystalline grains otherwise being void, making the organicsemiconducting layer less sensitive to air and moisture. For example,layers formed according to the process of the present invention showvery good stability in OFET devices in air.

The invention also provides an organic semiconducting layer whichcomprises the organic semiconducting layer formulation.

The invention further provides a process for preparing an organicsemiconducting layer, said process comprising the following steps:

-   (i) depositing on a substrate a liquid layer of a formulation    comprising one or more compounds of formula I as described above and    below, one or more organic binder resins or precursors thereof, and    optionally one or more solvents,-   (ii) forming from the liquid layer a solid layer which is the    organic semiconducting layer,-   (iii) optionally removing the layer from the substrate.

The process is described in more detail below.

The invention additionally provides an electronic device comprising thesaid organic semiconducting layer. The electronic device may include,without limitation, an organic field effect transistor (OFET), organiclight emitting diode (OLED), photodetector, sensor, logic circuit,memory element, capacitor or photovoltaic (PV) cell. For example, theactive semiconductor channel between the drain and source in an OFET maycomprise the layer of the invention. As another example, a charge (holeor electron) injection or transport layer in an OLED device may comprisethe layer of the invention. The formulations according to the presentinvention and layers formed therefrom have particular utility in OFETsespecially in relation to the preferred embodiments described herein.

In a preferred embodiment of the present invention the semiconductingcompound of formula I has a charge carrier mobility, μ, of more than10⁻⁵ cm²V⁻¹ s⁻¹, preferably of more than 10⁴ cm²V⁻¹ s⁻¹, more preferablyof more than 10⁻³ cm⁻²V⁻¹ s⁻¹, still more preferably of more than 10⁻²cm²V⁻¹ s⁻¹ and most preferably of more than 10⁻¹ cm²V⁻¹ s⁻¹.

The binder, which is typically a polymer, may comprise either aninsulating binder or a semiconducting binder, or mixtures thereof may bereferred to herein as the organic binder, the polymeric binder or simplythe binder.

Preferred binders according to the present invention are materials oflow permittivity, that is, those having a permittivity ∈ at 1,000 Hz of3.3 or less. The organic binder preferably has a permittivity ∈ at 1,000Hz of 3.0 or less, more preferably 2.9 or less. Preferably the organicbinder has a permittivity ∈ at 1,000 Hz of 1.7 or more. It is especiallypreferred that the permittivity of the binder is in the range from 2.0to 2.9. Whilst not wishing to be bound by any particular theory it isbelieved that the use of binders with a permittivity ∈ of greater than3.3 at 1,000 Hz, may lead to a reduction in the OSC layer mobility in anelectronic device, for example an OFET. In addition, high permittivitybinders could also result in increased current hysteresis of the device,which is undesirable.

An example of a suitable organic binder is polystyrene. Further examplesare given below.

In one type of preferred embodiment, the organic binder is one in whichat least 95%, more preferably at least 98% and especially all of theatoms consist of hydrogen, fluorine and carbon atoms.

It is preferred that the binder normally contains conjugated bonds,especially conjugated double bonds and/or aromatic rings.

The binder should preferably be capable of forming a film, morepreferably a flexible film. Polymers of styrene and α-methyl styrene,for example copolymers including styrene, α-methylstyrene and butadienemay suitably be used.

Binders of low permittivity of use in the present invention have fewpermanent dipoles which could otherwise lead to random fluctuations inmolecular site energies. The permittivity ∈ (dielectric constant) can bedetermined by the ASTM D150 test method.

It is also preferred that in the present invention binders are usedwhich have solubility parameters with low polar and hydrogen bondingcontributions as materials of this type have low permanent dipoles. Apreferred range for the solubility parameters (‘Hansen parameter’) of abinder for use in accordance with the present invention is provided inTable 1 below.

TABLE 1 Hansen parameter δ_(d) MPa^(1/2) δ_(p) MPa^(1/2) δ_(h) MPa^(1/2)Preferred range   14.5+  0-10 0-14 More preferred range 16+ 0-9 0-12Most preferred range 17+ 0-8 0-10

The three dimensional solubility parameters listed above include:dispersive (δ_(d)), polar (δ_(p)) and hydrogen bonding (δ_(h))components (C. M. Hansen, Ind. Eng. and Chem., Prod. Res. and Devl., 9,No 3, p 282, 1970). These parameters may be determined empirically orcalculated from known molar group contributions as described in Handbookof Solubility Parameters and Other Cohesion Parameters ed. A. F. M.Barton, CRC Press, 1991. The solubility parameters of many knownpolymers are also listed in this publication.

It is desirable that the permittivity of the binder has littledependence on frequency. This is typical of non-polar materials.Polymers and/or copolymers can be chosen as the binder by thepermittivity of their substituent groups. A list of suitable andpreferred low polarity binders is given (without limiting to theseexamples) in Table 2:

TABLE 2 typical low frequency Binder permittivity (ε) Polystyrene 2.5poly(α-methylstyrene) 2.6 poly(α-vinylnaphtalene) 2.6 poly(vinyltoluene)2.6 Polyethylene 2.2-2.3 cis-polybutadiene 2.0 Polypropylene 2.2Polyisoprene 2.3 poly(4-methyl-1-pentene) 2.1 poly (4-methylstyrene) 2.7poly(chorotrifluoroethylene) 2.3-2.8 poly(2-methyl-1,3-butadiene) 2.4poly(p-xylylene) 2.6 poly(α-α-α′-α′ tetrafluoro-p-xylylene) 2.4poly[1,1-(2-methyl propane)bis(4- 2.3 phenyl)carbonate] poly(cyclohexylmethacrylate) 2.5 poly(chlorostyrene) 2.6poly(2,6-dimethyl-1,4-phenylene ether) 2.6 Polyisobutylene 2.2poly(vinyl cyclohexane) 2.2 poly(vinylcinnamate) 2.9poly(4-vinylbiphenyl) 2.7

Other polymers suitable as binders include poly(1,3-butadiene) orpolyphenylene.

Especially preferred are formulations wherein the binder is selectedfrom poly-α-methyl styrene, polystyrene and polytriarylamine or anycopolymers of these, and the solvent is selected from xylene(s),toluene, tetralin and cyclohexanone.

Copolymers containing the repeat units of the above polymers are alsosuitable as binders. Copolymers offer the possibility of improvingcompatibility with the polyacene of formula I, modifying the morphologyand/or the glass transition temperature of the final layer composition.It will be appreciated that in the above table certain materials areinsoluble in commonly used solvents for preparing the layer. In thesecases analogues can be used as copolymers. Some examples of copolymersare given in Table 3 (without limiting to these examples). Both randomor block copolymers can be used. It is also possible to add some morepolar monomer components as long as the overall composition remains lowin polarity.

TABLE 3 typical low frequency Binder permittivity (ε)Poly(ethylene/tetrafluoroethylene) 2.6poly(ethylene/chlorotrifluoroethylene) 2.3 fluorinatedethylene/propylene copolymer   2-2.5 polystyrene-co-α-methylstyrene2.5-2.6 ethylene/ethyl acrylate copolymer 2.8 poly(styrene/10%butadiene) 2.6 poly(styrene/15% butadiene) 2.6 poly(styrene/2,4dimethylstyrene) 2.5 Topas ™ (all grades) 2.2-2.3

Other copolymers may include: branched or non-branchedpolystyrene-block-polybutadiene,polystyrene-block(polyethylene-ran-butylene)-block-polystyrene,polystyrene-block-polybutadiene-block-polystyrene,polystyrene-(ethylene-propylene)-diblock-copolymers (e.g.KRATON®-G1701E, Shell), poly(propylene-co-ethylene) andpoly(styrene-comethylmethacrylate).

Preferred insulating binders for use in the organic semiconductor layerformulation according to the present invention arepoly(α-methylstyrene), poiyvinylcinnamate, poly(4-vinylbiphenyl),poly(4-methylstyrene), and Topas™ 8007 (linear olefin,cyclo-olefin(norbornene) copolymer available from Ticona, Germany). Mostpreferred insulating binders are poly(α-methylstyrene),polyvinylcinnamate and poly(4-vinylbiphenyl).

The binder can also be selected from crosslinkable binders, like e.g.acrylates, epoxies, vinylethers, thiolenes etc., preferably having asufficiently low permittivity, very preferably of 3.3 or less. Thebinder can also be mesogenic or liquid crystalline.

As mentioned above the organic binder may itself be a semiconductor, inwhich case it will be referred to herein as a semiconducting binder. Thesemiconducting binder is still preferably a binder of low permittivityas herein defined. Semiconducting binders for use in the presentinvention preferably have a number average molecular weight (M_(n)) ofat least 1500-2000, more preferably at least 3000, even more preferablyat least 4000 and most preferably at least 5000. The semiconductingbinder preferably has a charge carrier mobility, μ, of at least 10⁻⁵cm²V⁻¹ s⁻¹, more preferably at least 10⁻⁴ cm²V⁻¹ s⁻¹.

A preferred class of semiconducting binder is a polymer as disclosed inU.S. Pat. No. 6,630,566, preferably an oligomer or polymer having repeatunits of formula 1:

wherein

-   Ar¹, Ar² and Ar³ which may be the same or different, denote,    independently if in different repeat units, an optionally    substituted aromatic group that is mononuclear or polynuclear, and-   m is an integer ≧1, preferably ≧6, preferably ≧10, more preferably    ≧15 and most preferably ≧20.

In the context of Ar¹, Ar² and Ar³, a mononuclear aromatic group hasonly one aromatic ring, for example phenyl or phenylene. A polynucleararomatic group has two or more aromatic rings which may be fused (forexample napthyl or naphthylene), individually covalently linked (forexample biphenyl) and/or a combination of both fused and individuallylinked aromatic rings. Preferably each Ar¹, Ar² and Ar³ is an aromaticgroup which is substantially conjugated over substantially the wholegroup.

Further preferred classes of semiconducting binders are those containingsubstantially conjugated repeat units. The semiconducting binder polymermay be a homopolymer or copolymer (including a block-copolymer) of thegeneral formula 2:

A_((c))B_((d)) . . . Z_((z))  2

wherein A, B, . . . , Z each represent a monomer unit and (c), (d), . .. (z) each represent the mole fraction of the respective monomer unit inthe polymer, that is each (c), (d), . . . (z) is a value from 0 to 1 andthe total of (c)+(d)+ . . . +(z)=1.

Examples of suitable and preferred monomer units A, B, . . . Z includeunits of formula 1 above and of formulae 3 to 8 given below (wherein mis as defined in formula 1:

wherein

-   R^(a) and R^(b) are independently of each other selected from H, F,    CN, NO₂, —N(R^(C))(R^(d)) or optionally substituted alkyl, alkoxy,    thioalkyl, acyl, aryl,-   R^(c) and R^(d) are independently or each other selected from H,    optionally substituted alkyl, aryl, alkoxy or polyalkoxy or other    substituents,    and wherein the asterisk (*) is any terminal or end capping group    including H, and the alkyl and aryl groups are optionally    fluorinated;

wherein

-   Y is Se, Te, O, S or —N(R^(e)), preferably O, S or —N(R^(e))—,-   R^(e) is H, optionally substituted alkyl or aryl,-   R^(a) and R^(b) are as defined in formula 3;

wherein R^(a), R^(b) and Y are as defined in formulae 3 and 4;

wherein R^(a), R^(b) and Y are as defined in formulae 3 and 4,

-   Z is —C(T¹)=C(T², —C≡C—, —N(R^(f))—, —N═N—, (R^(f))═N—,    —N═C(R^(f))—,-   T¹ and T² independently of each other denote H, Cl, F, —CN or lower    alkyl with 1 to 8 C atoms,-   R^(f) is H or optionally substituted alkyl or aryl;

wherein R^(a) and R^(b) are as defined in formula 3;

wherein R^(a), R^(b), R^(g) and R^(h) independently of each other haveone of the meanings of R^(a) and R^(b) in formula 3.

In the case of the polymeric formulae described herein, such as formulae1 to 8, the polymers may be terminated by any terminal group, that isany end-capping or leaving group, including H.

In the case of a block-copolymer, each monomer A, B, . . . Z may be aconjugated oligomer or polymer comprising a number, for example 2 to 50,of the units of formulae 3-8. The semiconducting binder preferablyincludes: arylamine, fluorene, thiophene, spiro bifluorene and/oroptionally substituted aryl (for example phenylene) groups, morepreferably arylamine, most preferably triarylamine groups. Theaforementioned groups may be linked by further conjugating groups, forexample vinylene.

In addition, it is preferred that the semiconducting binder comprises apolymer (either a homo-polymer or copolymer, including block-copolymer)containing one or more of the aforementioned arylamine, fluorene,thiophene and/or optionally substituted aryl groups. A preferredsemiconducting binder comprises a homo-polymer or copolymer (includingblock-copolymer) containing arylamine (preferably triarylamine) and/orfluorene units. Another preferred semiconducting binder comprises ahomo-polymer or co-polymer (including block-copolymer) containingfluorene and/or thiophene units.

The semiconducting binder may also contain carbazole or stilbene repeatunits. For example polyvinylcarbazole or polystilbene polymers orcopolymers may be used. The semiconducting binder may optionally containpolyacene segments (for example repeat units as described for formula Iabove) to improve compatibility with the soluble polyacene molecules.

The most preferred semiconducting binders for use in the organicsemiconductor layer formulation according to the present invention arepoly(9-vinylcarbazole) and PTAA1, a polytriarylamine of the followingformula

wherein m is as defined in formula 1.

For application of the semiconducting layer in p-channel FETs, it isdesirable that the semiconducting binder should have a higher ionisationpotential than the semiconducting compound of formula 1, otherwise thebinder may form hole traps. In n-channel materials the semiconductingbinder should have lower electron affinity than the n-type semiconductorto avoid electron trapping.

The formulation according to the present invention may be prepared by aprocess which comprises:

-   (i) first mixing a compound of formula I and an organic binder or a    precursor thereof. Preferably the mixing comprises mixing the two    components together in a solvent or solvent mixture,-   (ii) applying the solvent(s) containing the compound of formula I    and the organic binder to a substrate; and optionally evaporating    the solvent(s) to form a solid organic semiconducting layer    according to the present invention,-   (iii) and optionally removing the solid layer from the substrate or    the substrate from the solid layer.

In step (i) the solvent may be a single solvent or the compound offormula I and the organic binder may each be dissolved in a separatesolvent followed by mixing the two resultant solutions to mix thecompounds.

The binder may be formed in situ by mixing or dissolving a compound offormula I in a precursor of a binder, for example a liquid monomer,oligomer or crosslinkable polymer, optionally in the presence of asolvent, and depositing the mixture or solution, for example by dipping,spraying, painting or printing it, on a substrate to form a liquid layerand then curing the liquid monomer, oligomer or crosslinkable polymer,for example by exposure to radiation, heat or electron beams, to producea solid layer. If a preformed binder is used it may be dissolvedtogether with the compound of formula I in a suitable solvent, and thesolution deposited for example by dipping, spraying, painting orprinting it on a substrate to form a liquid layer and then removing thesolvent to leave a solid layer. It will be appreciated that solvents arechosen which are able to dissolve both the binder and the compound offormula I, and which upon evaporation from the solution blend give acoherent defect free layer.

Suitable solvents for the binder or the compound of formula I can bedetermined by preparing a contour diagram for the material as describedin ASTM Method D 3132 at the concentration at which the mixture will beemployed. The material is added to a wide variety of solvents asdescribed in the ASTM method.

It will also be appreciated that in accordance with the presentinvention the formulation may also comprise two or more compounds offormula I and/or two or more binders or binder precursors, and that theprocess for preparing the formulation may be applied to suchformulations.

Examples of suitable and preferred organic solvents include, withoutlimitation, dichloromethane, trichloromethane, monochlorobenzene,o-dichlorobenzene, tetrahydrofuran, anisole, morpholine, toluene,o-xylene, m-xylene, p-xylene, 1,4-dioxane, acetone, methylethylketone,1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane,ethyl acetate, n-butyl acetate, dimethylformamide, dimethylacetamide,dimethylsulfoxide, tetralin, decalin, indane and/or mixtures thereof.

After the appropriate mixing and ageing, solutions are evaluated as oneof the following categories: complete solution, borderline solution orinsoluble. The contour line is drawn to outline the solubilityparameterhydrogen bonding limits dividing solubility and insolubility.‘Complete’ solvents falling within the solubility area can be chosenfrom literature values such as published in “Crowley, J. D., Teague, G.S. Jr and Lowe, J. W. Jr., Journal of Paint Technology, 38, No 496, 296(1966)”. Solvent blends may also be used and can be identified asdescribed in “Solvents, W. H. Ellis, Federation of Societies forCoatings Technology, p 9-10, 1986”. Such a procedure may lead to a blendof ‘non’ solvents that will dissolve both the binder and the compound offormula I, although it is desirable to have at least one true solvent ina blend.

Especially preferred solvents for use in the formulation according tothe present invention, with insulating or semiconducting binders andmixtures thereof, are xylene(s), toluene, tetralin ando-dichlorobenzene.

The proportions of binder to the compound of formula I in theformulation or layer according to the present invention are typically20:1 to 1:20 by weight, preferably 10:1 to 1:10 more preferably 5:1 to1:5, still more preferably 3:1 to 1:3 further preferably 2:1 to 1:2 andespecially 1:1. Surprisingly and beneficially, dilution of the compoundof formula I in the binder has been found to have little or nodetrimental effect on the charge mobility, in contrast to what wouldhave been expected from the prior art.

In accordance with the present invention it has further been found thatthe level of the solids content in the organic semiconducting layerformulation is also a factor in achieving improved mobility values forelectronic devices such as OFETs. The solids content of the formulationis commonly expressed as follows:

${{Solids}\mspace{14mu} {content}\mspace{14mu} (\%)} = {\frac{a + b}{a + b + c} \times 100}$

whereina=mass of compound of formula I, b=mass of binder and c=mass of solvent.

The solids content of the formulation is preferably 0.1 to 10% byweight, more preferably 0.5 to 5% by weight.

Surprisingly and beneficially, dilution of the compound of formula I inthe binder has been found to have little or no effect on the chargemobility, in contrast to what would have been expected from the priorart.

It is desirable to generate small structures in modern microelectronicsto reduce cost (more devices/unit area), and power consumption.Patterning of the layer of the invention may be carried out byphotolithography or electron beam lithography.

Liquid coating of organic electronic devices such as field effecttransistors is more desirable than vacuum deposition techniques. Theformulations of the present invention enable the use of a number ofliquid coating techniques. The organic semiconductor layer may beincorporated into the final device structure by, for example and withoutlimitation, dip coating, spin coating, ink jet printing, letter-pressprinting, screen printing, doctor blade coating, roller printing,reverse-roller printing, offset lithography printing, flexographicprinting, web printing, spray coating, brush coating or pad printing.The present invention is particularly suitable for use in spin coatingthe organic semiconductor layer into the final device structure.

Selected formulations of the present invention may be applied toprefabricated device substrates by ink jet printing or microdispensing.Preferably industrial piezoelectric print heads such as but not limitedto those supplied by Aprion, Hitachi-Koki, InkJet Technology, On TargetTechnology, Picojet, Spectra, Trident, Xaar may be used to apply theorganic semiconductor layer to a substrate. Additionally semi-industrialheads such as those manufactured by Brother, Epson, Konica, SeikoInstruments Toshiba TEC or single nozzle microdispensers such as thoseproduced by Microdrop and Microfab may be used.

In order to be applied by ink jet printing or microdispensing, themixture of the compound of formula I and the binder should be firstdissolved in a suitable solvent. Solvents must fulfil the requirementsstated above and must not have any detrimental effect on the chosenprint head. Additionally, solvents should have boiling points >100° C.,preferably >140° C. and more preferably >150° C. in order to preventoperability problems caused by the solution drying out inside the printhead. Suitable solvents include substituted and non-substituted xylenederivatives, di-C₁₋₂-alkyl formamide, substituted and non-substitutedanisoles and other phenol-ether derivatives, substituted heterocyclessuch as substituted pyridines, pyrazines, pyrimidines, pyrrolidinones,substituted and non-substituted N,N-di-C₁₋₂-alkylanilines and otherfluorinated or chlorinated aromatics.

A preferred solvent for depositing a formulation according to thepresent invention by ink jet printing comprises a benzene derivativewhich has a benzene ring substituted by one or more substituents whereinthe total number of carbon atoms among the one or more substituents isat least three. For example, the benzene derivative may be substitutedwith a propyl group or three methyl groups, in either case there beingat least three carbon atoms in total. Such a solvent enables an ink jetfluid to be formed comprising the solvent with the binder and thecompound of formula I which reduces or prevents clogging of the jets andseparation of the components during spraying. The solvent(s) may includethose selected from the following list of examples: dodecylbenzene,1-methyl-4-tert-butylbenzene, terpineol limonene, isodurene,terpinolene, cymene, diethylbenzene. The solvent may be a solventmixture, that is a combination of two or more solvents, each solventpreferably having a boiling point >100° C., more preferably >140° C.Such solvent(s) also enhance film formation in the layer deposited andreduce defects in the layer.

The ink jet fluid (that is mixture of solvent, binder and semiconductingcompound) preferably has a viscosity at 20° C. of 1-100 mPa·s, morepreferably 1-50 mPa·s and most preferably 1-30 mPa·s.

The use of the binder in the present invention also allows the viscosityof the coating solution to be tuned to meet the requirements of theparticular print head.

The semiconducting layer of the present invention is typically at most 1micron (=1 μm) thick, although it may be thicker if required. The exactthickness of the layer will depend, for example, upon the requirementsof the electronic device in which the layer is used. For use in an OFETor OLED, the layer thickness may typically be 500 nm or less.

In the semiconducting layer of the present invention there may be usedtwo or more different compounds of formula 1. Additionally oralternatively, in the semiconducting layer there may be used two or moreorganic binders of the present invention.

As mentioned above, the invention further provides a process forpreparing the organic semiconducting layer which comprises (i)depositing on a substrate a liquid layer of a formulation whichcomprises one or more compounds of formula I, one or more organicbinders or precursors thereof and optionally one or more solvents, and(ii) forming from the liquid layer a solid layer which is the organicsemiconducting layer.

In the process, the solid layer may be formed by evaporation of thesolvent and/or by reacting the binder resin precursor (if present) toform the binder resin in situ. The substrate may include any underlyingdevice layer, electrode or separate substrate such as silicon wafer orpolymer substrate for example.

In a particular embodiment of the present invention, the binder may bealignable, for example capable of forming a liquid crystalline phase. Inthat case the binder may assist alignment of the compound of formula 1,for example such that the polyacene backbone is preferentially alignedalong the direction of charge transport. Suitable processes for aligningthe binder include those processes used to align polymeric organicsemiconductors and are described in prior art, for example in WO03/007397 (Plastic Logic).

The formulation according to the present invention can additionallycomprise one or more further components like for example surface-activecompounds, lubricating agents, wetting agents, dispersing agents,hydrophobing agents, adhesive agents, flow improvers, defoaming agents,deaerators, diluents, reactive or non-reactive diluents, auxiliaries,colourants, dyes or pigments, furthermore, especially in casecrosslinkable binders are used, catalysts, sensitizers, stabilizers,inhibitors, chain-transfer agents or co-reacting monomers.

The present invention also provides the use of the semiconductingcompound, formulation or layer in an electronic device. The formulationmay be used as a high mobility semiconducting material in variousdevices and apparatus. The formulation may be used, for example, in theform of a semiconducting layer or film. Accordingly, in another aspect,the present invention provides a semiconducting layer for use in anelectronic device, the layer comprising the formulation according to theinvention. The layer or film may be less than about 30 microns. Forvarious electronic device applications, the thickness may be less thanabout 1 micron thick. The layer may be deposited, for example on a partof an electronic device, by any of the aforementioned solution coatingor printing techniques.

The compound or formulation may be used, for example as a layer or film,in a field effect transistor (FET) for example as the semiconductingchannel, organic light emitting diode (OLED) for example as a hole orelectron injection or transport layer or electroluminescent layer,photodetector, chemical detector, photovoltaic cell (PVs), capacitorsensor, logic circuit, display, memory device and the like. The compoundor formulation may also be used in electrophotographic (EP) apparatus.The compound or formulation is preferably solution coated to form alayer or film in the aforementioned devices or apparatus to provideadvantages in cost and versatility of manufacture. The improved chargecarrier mobility of the compound or formulation of the present inventionenables such devices or apparatus to operate faster and/or moreefficiently. The compound, formulation and layer of the presentinvention are especially suitable for use in an organic field effecttransistor OFET as the semiconducting channel. Accordingly, theinvention also provides an organic field effect transistor (OFET)comprising a gate electrode, an insulating (or gate insulator) layer, asource electrode, a drain electrode and an organic semiconductingchannel connecting the source and drain electrodes, wherein the organicsemiconducting channel comprises an organic semiconducting layeraccording to the present invention. Other features of the OFET are wellknown to those skilled in the art.

The gate, source and drain electrodes and the insulating andsemiconducting layer in the OFET device may be arranged in any sequence,provided that the source and drain electrode are separated from the gateelectrode by the insulating layer, the gate electrode and thesemiconductor layer both contact the insulating layer, and the sourceelectrode and the drain electrode both contact the semiconducting layer.

An OFET device according to the present invention preferably comprises:

-   -   a source electrode,    -   a drain electrode,    -   a gate electrode,    -   a semiconducting layer,    -   one or more gate insulator layers,    -   optionally a substrate.        wherein the semiconductor layer preferably comprises a polyacene        compound, preferably a compound of formula I, very preferably a        formulation comprising a polyacene compound of formula I and an        organic binder as described above and below.

The OFET device can be a top gate device or a bottom gate device.Suitable structures and manufacturing methods of an OFET device areknown to the skilled in the art and are described in the literature, forexample in WO 03/052841.

The gate insulator layer preferably comprises a fluoropolymer, like e.g.the commercially available Cytop 809M® or Cytop 107M® (from AsahiGlass). Preferably the gate insulator layer is deposited, e.g. byspin-coating, doctor blading, wire bar coating, spray or dip coating orother known methods, from a formulation comprising an insulator materialand one or more solvents with one or more fluoro atoms (fluorosolvents),preferably a perfluorosolvent. A suitable perfluorosolvent is e.g. FC75®(available from Acros, catalogue number 12380). Other suitablefluoropolymers and fluorosolvents are known in prior art, like forexample the perfluoropolymers Teflon AF® 1600 or 2400 (from DuPont) orFluoropel® (from Cytonix) or the perfluorosolvent FC 43® (Acros, No.12377).

Unless the context clearly indicates otherwise, as used herein pluralforms of the terms herein are to be construed as including the singularform and vice versa.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, mean “including but not limited to”, andare not intended to (and do not) exclude other components.

It will be appreciated that variations to the foregoing embodiments ofthe invention can be made while still falling within the scope of theinvention. Each feature disclosed in this specification, unless statedotherwise, may be replaced by alternative features serving the same,equivalent or similar purpose. Thus, unless stated otherwise, eachfeature disclosed is one example only of a generic series of equivalentor similar features.

All of the features disclosed in this specification may be combined inany combination, except combinations where at least some of suchfeatures and/or steps are mutually exclusive. In particular, thepreferred features of the invention are applicable to all aspects of theinvention and may be used in any combination. Likewise, featuresdescribed in non-essential combinations may be used separately (not incombination).

It will be appreciated that many of the features described above,particularly of the preferred embodiments, are inventive in their ownright and not just as part of an embodiment of the present invention.Independent protection may be sought for these features in addition toor alternative to any invention presently claimed.

The invention will now be described in more detail by reference to thefollowing examples, which are illustrative only and do not limit thescope of the invention.

The following parameters are used:

μ is the charge carrier mobilityW is the length of the drain and source electrodeL is the distance of the drain and source electrodeI_(DS) is the source-drain currentC_(i) is the capacitance per unit area of the gate dielectricV_(G) is the gate voltage (in V)V_(DS) is the source-drain voltageV₀ is the offset voltage

Unless stated otherwise, all specific values of physical parameters likethe permittivity (∈), charge carrier mobility (μ), solubility parameter(δ) and viscosity (η) as given above and below refer to a temperature of20° C. (+/−1° C.).

EXAMPLE 1 Compound (1)(2,3-dimethyl-6,13-bis(triisopropylsilylethynyl)pentacene) is PreparedAccording to the Method Described in Schemes 1-4 Above

1,4-Anthracenedione

To a solution of quinizarin (10.00 g, 42.0 mmol, 1 molar equivalent) inmethanol (200 mL) cooled to −0° C. was added sodium borohydride (6.38 g,169.0 mmol, 4 molar equivalent). The resulting mixture was stirred at−0° C. for 2 h. A solution of 5M hydrochloric acid (150 mL) was thenadded dropwise to the reaction mixture at −0° C. The precipitated orangesolid was filtered, washed twice with water, and dried under vacuum.Purification by column chromatography on silica gel (eluent:dichloromethane) gave the title compound as yellow needles (5.9 g, 68%).¹H NMR (300.13 MHz, CDCl₃)

(ppm) 7.08 (s, 2H) 7.68-7.72 (m, 2H) 8.05-8.10 (m, 2H) 8.63 (s, 2H).

1,4-Dihydroxyanthracene

A solution of sodium hydrosulfite (16.70 g, 42.0 mmol, 1 molarequivalent) in a water/dioxane (3/2) (250 mL) mixture was added undernitrogen to the 1,4-anthracenedione 1 (5.00 g, 24.0 mmol, 1 molarequivalent). The resulting mixture was stirred at room temperature for 3h. Water was added and the resulting precipitate was filtered, washedwith water and dried under vacuum to give the title compound as a yellowpowder (3.10 g, 61%). ¹H NMR (300.13 MHz, THF-d₈) δ (ppm) 6.53 (s, 2H)7.34-7.40 (m, 2H) 7.96-7.99 (m, 2H) 8.65 (s, 2H) 8.70 (s, 2H).

4,5-Dimethylphthalaldehyde

To a solution of oxalyl chloride 2M in dichloromethane (DCM) (26.5 mL,53.0 mmol, 2.2 molar equivalents) cooled to −78° C. was added dropwise asolution of dimethylsulfoxide (DMSO) (7.5 mL, 105.8 mmol; 4.4 molarequivalents) in DCM (10 ml). The solution was stirred at −78° C. for 5min and 4,5-dimethylbenzene-1,2-dimethanol (4.0 g, 24.1 mmol, 1.0 molarequivalent) dissolved in a mixture of DCM-DMSO (2 ml-4 ml) was addeddropwise. The solution was stirred for 1 h at −78° C. and triethylamine(20 mL) was slowly added at −78° C. The reaction mixture was stirred 10minutes at −78° C. and slowly warmed up to room temperature. Ice-coldwater (100 ml) was added to the reaction mixture and the aqueous layerextracted with DCM (3×100 ml). The organic fractions were combined,dried over magnesium sulfate, filtered and concentrated in vacuum togive a brown oil. Purification by column chromatography on silica gel(eluent: hexane-ethyl acetate 8/2) gave the title compound as whiteneedles (3.2 g, 82%). ¹H NMR (300.13 MHz, CDCl₃)

(ppm) 2.42 (s, 6H) 7.73 (s, 2H) 10.50 (s, 2H).

2,3-Dimethyl-6,13-pentacenequinone

To a solution of 4,5-dimethylphthalaldehyde 3 (0.25 g, 1.5 mmol, 1 molarequivalent) and 1,4-dihydroxyanthracene 2 (0.33 g, 1.6 mmol, 1 molarequivalent) in ethanol (40 ml) was added a solution of 5% aqueous NaOH(2 ml) at room temperature. The reaction mixture was stirred 30 minutesat room temperature and then warmed to 60° C. After 1 hour at 60° C.,the reaction mixture was cooled to room temperature. The resultingprecipitate was filtered, washed with water (15 ml), a mixtureethanol/water (20 ml) and ethanol (20 ml) to give the title compound asa yellow powder (0.42 g, 80%) used as obtained.

2,3-Dimethyl-6,13-bis(triisopropylsilylethynyl)pentacene

To a solution of triisopropylsilylacetylene (1.6 mL, 7.1 mmol, 6 molarequivalents) in tetrahydrofurane (40 ml) cooled to −78° C. was addeddropwise a 2.5M solution of n-butyllithium in hexane (2.6 mL, 6.5 mmol,5.5 molar equivalents). The solution was stirred at −78° C. for 45 minand 2,3-dimethyl-6,13-pentacenequinone 4 (0.4 g, 1.2 mmol, 1 molarequivalent) was added. The reaction mixture was warmed up and stirredovernight at room temperature. A solution of 10% aqueous HCl saturatedwith SnCl₂ (4 ml) was added at room temperature and the reaction mixturewas stirred at 50° C. for 45 min. After cooling a solution of 2M aqueoussolution of Na₂CO₃ (4 ml) was added to the reaction mixture and theresulting solution was stirred with celite for 5 min. The solution wasfiltered through celite and concentrated under vacuum to give a darkblue solid. Purification by column chromatography on silica gel (eluent:hexane-DCM 1/9) followed by an acetone wash gave the title compound as adark blue powder (0.26 g, 37%). >99% Pure by HPLC. ¹H NMR (300.13 MHz,CDCl₃)

(ppm) 1.32-1.46 (m, 42H) 2.48 (s, 6H) 7.37-7.41 (m, 2H) 7.70 (s, 2H)7.94-7.97 (m, 2H) 9.14 (s, 2H) 9.28 (s, 2H). ¹³C NMR (125.77 MHz, CDCl₃)δ (ppm) 11.71, 19.02, 20.56, 104.91, 106.69, 118.01, 124.58, 125.82,126.20, 127.09, 128.67, 130.49, 132.01, 136.60.

EXAMPLE 2 Compound (2)(5,12-bis(triisopropylsilylethynyl)tetracene[2,3-b]thiophene is PreparedAccording to the Method Described in Scheme 1-4 Above

Tetracene[2,3-b]thiophene-5,12-dione

To a solution of 2,3-thiophenedicarboxaldehyde (0.20 g, 1.4 mmol, 1molar equivalent) and 1,4-dihydroxyanthracene 2 (0.30 g, 1.4 mmol, 1molar equivalent) in ethanol (30 ml) was added a solution of 5% aqueousNaOH (2 ml) at room temperature. The reaction mixture was stirred 30minutes at room temperature and then warmed to 60° C. After 1 hour at60° C., the reaction mixture was cooled to room temperature. Theresulting precipitate was filtered, washed with water (15 ml), a mixtureethanol/water (20 ml) and ethanol (20 ml) to give the title compound asa yellow powder (0.37 g, 82%) used as obtained.

5,12-bis(triisopropylsilylethynyl)tetracene[2,3-b]thiophene

To a solution of triisopropylsilylacetylene (1.5 mL, 6.7 mmol, 6 molarequivalents) in tetrahydrofurane (THF) (40 ml) cooled to −78° C. wasadded dropwise a 2.5M solution of n-butyllithium in hexane (2.5 mL, 6.1mmol, 5.5 molar equivalents). The solution was stirred at −78° C. for 45min and tetracene[2,3-b]thiophene-5,12-dione 6 (0.35 g, 1.1 mmol, 1molar equivalent) was added. The reaction mixture was warmed up andstirred overnight at room temperature. A solution of 10% aqueous HClsaturated with SnCl₂ (4 ml) was added at room temperature and thereaction mixture was stirred at 50° C. for 45 min. After cooling asolution of 2M aqueous solution of Na₂CO₃ (4 ml) was added to thereaction mixture and the resulting solution was stirred with celite for5 min. The solution was filtered through celite and concentrated undervacuum to give a dark blue solid. Purification by column chromatographyon silica gel (eluent: hexane-DCM 95/5) followed by an acetone wash gavethe title compound as a dark purple powder (0.25 g, 35%). >99% Pure byHPLC. ¹H NMR (300.13 MHz, CDCl₃)

(ppm) 1.32-1.43 (m, 42H) 7.40-7.45 (m, 3H) 7.53 (d, 1H, J=5.7 Hz)7.98-8.01 (m, 2H) 9.14 (s, 1H) 9.17 (s, 1H) 9.32 (s, 2H). ¹³C NMR(125.77 MHz, CDCl₃)

(ppm) 11.67, 18.98, 104.38, 104.46, 106.32, 106.64, 117.30, 118.67,120.07, 121.39, 123.78, 125.90, 125.95, 126.21, 126.24, 128.59, 128.62,130.04, 130.15, 130.30, 130.43, 132.06, 132.15, 139.71, 140.24.

FET Measurements

The field effect mobility of the following organic semiconductormaterials is tested using the techniques described by Holland et al, J.Appl. Phys. Vol. 75, p. 7954 (1994).

In the following examples a test field effect transistor is manufacturedby using a PEN substrate upon which are patterned Pt/Pd source and drainelectrodes by standard techniques, for example shadow masking.Semiconductor formulations are prepared using the organic semiconductorcompound (here compound (1) of example 1 and compound (2) of example 2,respectively) blended with an inert polymeric binder resin (herepoly(alpha-methylstyrene), Aldrich catalogue number 19, 184-1). Thesemiconductor formulations are then dissolved one part into 99 parts ofsolvent (here p-Xylene), and spin coated onto the substrate at 500 rpmfor 18 seconds. To ensure complete drying, the samples are placed in anoven for 20 minutes at 100° C.

For comparison, films of the symmetric pentacene compound6,13-bis(triisopropylsilylethynyl)pentacene (TIPS) are coated by spincoating. These are then dried in an oven for 20 minutes at 100° C.

The insulator material (Cytop 809M®, a formulation of a fluoropolymer ina fluorosolvent, available from Asahi Glass) is spin-coated onto thesemiconductor giving a thickness typically of approximately 1 μm. Thesamples are placed once more in an oven at 100° C. for 20 minutes toevaporate solvent from the insulator. A gold gate contact is definedover the device channel area by evaporation through a shadow mask. Todetermine the capacitance of the insulator layer a number of devices areprepared which consist of a non-patterned Pt/Pd base layer, an insulatorlayer prepared in the same way as that on the FET device, and a topelectrode of known geometry. The capacitance is measured using ahand-held multimeter, connected to the metal either side of theinsulator. Other defining parameters of the transistor are the length ofthe drain and source electrodes facing each other (W=30 mm) and theirdistance from each other (L=130 μm).

The voltages applied to the transistor are relative to the potential ofthe source electrode. In the case of a p-type gate material, when anegative potential is applied to the gate, positive charge carriers(holes) are accumulated in the semiconductor on the other side of thegate dielectric. (For an n-channel FET, positive voltages are applied).This is called the accumulation mode. The capacitance per unit area ofthe gate dielectric C_(i) determines the amount of the charge thusinduced. When a negative potential V_(DS) is applied to the drain, theaccumulated carriers yield a source-drain current I_(DS) which dependsprimarily on the density of accumulated carriers and, importantly, theirmobility in the source-drain channel. Geometric factors such as thedrain and source electrode configuration, size and distance also affectthe current. Typically a range of gate and drain voltages are scannedduring the study of the device. The source-drain current is described byEquation (1).

$\begin{matrix}{I_{DS} = {{\frac{\mu \; {WC}_{i}}{L}\left( {{\left( {V_{G} - V_{0}} \right)V_{DS}} - \frac{V_{DS}^{2}}{2}} \right)} + I_{\Omega}}} & (1)\end{matrix}$

where V₀ is an offset voltage and I_(Ω) is an ohmic current independentof the gate voltage and is due to the finite conductivity of thematerial. The other parameters are as defined above.

For the electrical measurements the transistor sample is mounted in asample holder. Microprobe connections are made to the gate, drain andsource electrodes using Karl Suss PH100 miniature probe-heads. These arelinked to a Hewlett-Packard 4155B parameter analyser. The drain voltageis set to −5 V and the gate voltage is scanned from +20 to −60V and backto +20V in 1 V steps. In accumulation, when |V_(G)|>|V_(DS)| thesource-drain current varies linearly with V_(G). Thus the field effectmobility can be calculated from the gradient (S) of I_(DS) vs. V_(G)given by Equation (2).

$\begin{matrix}{S = \frac{\mu \; {WC}_{i}V_{DS}}{L}} & (2)\end{matrix}$

All field effect mobilities quoted below are calculated using thisregime (unless stated otherwise). Where the field effect mobility varieswith gate voltage, the value is taken as the highest level reached inthe regime where |V_(G)|>|V_(DS)| in accumulation mode. The valuesquoted below are an average taken over several devices (fabricated onthe same substrate), Examples of the current-voltage andmobility-voltage characteristics for example 1 and 2 are shown in FIGS.1 and 2, respectively. The forward and reverse scans illustrate the lowcurrent hysteresis of the device.

USE EXAMPLE 1

For this purpose compound (1) is dissolved with poly-α-methylstyrene(1:1) at 1% total solids in m-Xylene. The resulting solution is thenspin coated upon masked Pt/Pd patterned source/drain electrodes. Cytop809M® is used as the gate insulator. Compound (1) gives an averagemobility of 0.13 cm²/Vs (+/−0.02). Average I_(On)/I_(Off) ratio=75,000.

FIG. 1 shows the transfer curves for use example 1 with forward andreverse scans, and illustrates the very low level of hysteresis in thedevices.

COMPARATIVE EXAMPLE 1

An FET is manufactured from a solution of pure compound (1) (1% inm-xylene) without a binder. Compound (1) gives an average mobility of0.051 cm²/Vs (Standard deviation=0.19). I_(On)/I_(Off) ratio=3100. Thetransfer characteristics are shown in FIG. 3.

USE EXAMPLE 2

Compound (2) is dissolved with poly-α-methylstyrene (1:1) at 4% totalsolids in m-Xylene. The resulting solution is then spin coated uponmasked Pt/Pd patterned source/drain electrodes. Cytop 809M® is used asthe gate insulator. Compound (2) gives an average mobility of 0.46cm²/Vs Vs (+/−0.09). Average I_(On)/I_(Off) ratio=267,000.

FIG. 2 shows the transfer curves for use example 2 with forward andreverse scans, and illustrates the very low level of hysteresis in thedevices.

COMPARATIVE EXAMPLE 2

An FET is manufactured from a solution of the symmetric compound6,13-bis(triisopropylsilylethynyl)pentacene (TIPS) (4% in m-xylene)without a binder. TIPS gives an average mobility of 0.06 cm²Vs (19).Average I_(On)/I_(Off) ratio=94,660. The transfer characteristics areshown in FIG. 4.

The results show the excellent charge mobility of OFET devices when acompound according to formula I of the present invention is used asorganic semiconductor together with an organic binder.

1. Compounds of formula I

wherein n is 0, 1, 2, 3, 4 or 5, R¹⁻¹² denote, in case of multipleoccurrence independently of one another, identical or different groupsselected from H, halogen, —CN, —NC, —NCO, —NCS, —OCN, —SCN,—C(═O)NR⁰R⁰⁰, —C(═O)X, —C(═O)R⁰, —NH₂, —NR⁰R⁰⁰, —SH, —SR⁰, —SO₃H,—SO₂R⁰, —OH, —NO₂, —CF₃, —SF₅, optionally substituted silyl, or carbylor hydrocarbyl with 1 to 40 C atoms that is optionally substituted andoptionally comprises one or more hetero atoms, wherein at least twogroups R¹⁻¹² that are present in the compound are different from H, X ishalogen, R⁰ and R⁰⁰ are independently of each other H or an optionallysubstituted carbyl or hydrocarbyl group optionally comprising one ormore hetero atoms, optionally two or more of the substituents R¹-R¹²,which are located on adjacent ring positions of the polyacene,constitute a further saturated, unsaturated or aromatic ring systemhaving 4 to 40 C atoms, which is monocyclic or polycyclic, is fused tothe polyacene, is optionally intervened by one or more groups selectedfrom —O—, —S— and —N(R⁰)—, and is optionally substituted by one or moreidentical or different groups R¹, optionally one or more of the carbonatoms in the polyacene skeleton or in the rings formed by R¹⁻¹² arereplaced by a heteroatom selected from N, P, As, O, S, Se and Te,wherein the compounds do not have a symmetry axis or symmetry planeperpendicular to their long molecular axis, with the provisos that a) ifn is 2, then R⁶ and R¹¹ are different from H, and/or b) if n is 1, thenR¹, R⁴, R⁶ and R¹¹ are not identical groups and R⁵, R⁷, R¹⁰ and R¹² arenot identical groups, and/or c) if n is 1, then the groups R² and R³ andthe groups R⁸ and R⁹ do not form a thiophene ring with the polyacene, d)if n is 0, then R⁵ and R¹² are different from H, and/or e) if n is 2,then R² and R³ are different from COOCH₃.
 2. Compounds according toclaim 1, characterized in that n is 0 and R⁵ and R¹² are different fromH.
 3. Compounds according to claim 1, characterized in that n is 1 andR⁵ and R¹² are different from H.
 4. Compounds according to claim 1,characterized in that n is 2 and R⁶ and R¹² are different from H. 5.Compounds according to claim 1, characterized in that R² and R³ aredifferent from H, and R⁸ and R⁹ are different from R² and R³. 6.Compounds according to claim 1, characterized in that the groups R² andR³ and/or the groups R⁸ and R⁹ together with the polyacene form a 5-, 6-or 7-membered aromatic or heteroaromatic ring selected from pyridine,pyrimidine, thiophene, selenophene, thiazole, thiadiazole, oxazole andoxadiazole
 7. Compounds according to claim 6, characterized in that thegroups R² and R³ and/or the groups R⁸ and R⁹ together with the polyaceneform a ring selected from the following groups or their mirror images(wherein the asterisks denote the positions where the respective groupis fused to the polyacene)


8. Compounds according to claim 1, characterized in that at least two ofR¹⁻¹², in case n=0 or 1 R⁵ and R¹², and in case n=2 R⁶ and R¹¹, denote—C≡C-MR′R″R′″ or —C≡C-MR′R″″, wherein M is Si or Ge, R′, R″ and R′″ areidentical or different groups selected from H, a C₁-C₄₀-alkyl group, aC₆-C₄₀-aryl group, a C₆-C₄₀-arylalkyl group, a C₁-C₄₀-alkoxy group, or aC₆-C₄₀-arylalkyloxy group, R″″ forms a cyclic silyl alkyl group togetherwith the M atom, wherein all these groups are optionally substituted. 9.Compounds according to claim 1, characterized in that they are selectedfrom the following formulae

wherein R¹⁻¹² are as defined in formula I and A and B are independentlyof each other a saturated, unsaturated or aromatic ring system having 4to 40 C atoms, which is monocyclic or polycyclic, is fused to thepolyacene, is optionally intervened by one or more groups selected from—O—, —S— and —N(R⁰)—, and is optionally substituted by one or moreidentical or different groups R¹.
 10. Compounds according to claim 9,characterized in that they are selected from the following formulae

wherein R^(1a), R^(2a), R^(3a), R^(4a), R^(8a) and R^(9a) have one ofthe meanings of R¹ as given in formula I, R^(5a), R^(6a), R^(11a) andR^(12a) denote —C≡C-MR′R″R′″ or —C≡C-MR′R″″ as defined in claim 8 andR^(13a) and R^(14a) denote C₁-C₄₀-alkyl group that is optionallysubstituted.
 11. Formulation comprising one or more compounds accordingto claim 1, one or more organic binders or precursors thereof, andoptionally one or more solvents.
 12. Formulation according to claim 11,characterized in that the organic binder has a permittivity ∈ at 1,000Hz of 3.3 or less.
 13. Formulation according to claim 1, characterizedin that it comprises one or more binders selected from styrene, α-methylstyrene, copolymers including one or more of styrene, α-methylstyreneand butadiene, or precursors thereof.
 14. Formulation according to claim1, characterized in that it comprises one or more organic solventsselected from dichloromethane, trichloromethane, monochlorobenzene,o-dichlorobenzene, tetrahydrofuran, anisole, morpholine, toluene,o-xylene, m-xylene, p-xylene, 1,4-dioxane, acetone, methylethylketone,1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane,ethyl acetate, n-butyl acetate, dimethylformamide, dimethylacetamide,dimethylsulfoxide, tetralin, decalin, indane and/or mixtures thereof.15. Organic semiconducting layer comprising one or more compounds orformulations according to claim
 1. 16. Process for preparing an organicsemiconducting layer according to claim 15, comprising the followingsteps (i) depositing on a substrate a liquid layer of a formulationaccording to at least one of the preceding claims, (ii) forming from theliquid layer a solid layer which is the organic semiconducting layer,(iii) optionally removing the layer from the substrate.
 17. Process ofpreparing an unsymmetrical polyacene by reacting an anthracene-1,4-diolwith an optionally substituted phthalaldehyde or an optionallysubstituted heteroaromatic dicarboxaldehyde in the presence of a base.18. Use of a compound, formulation or layer according to claim 1 in anelectronic, optical or electrooptical component or device. 19.Electronic, optical or electrooptical component or device comprising oneor more compounds, formulations or layers according to claim
 1. 20.Organic field effect transistor (OFET), thin film transistor (TFT),component of integrated circuitry (IC), radio frequency identification(RFID) tag, organic light emitting diode (OLED), electroluminescentdisplay, flat panel display, backlight, photodetector, sensor, logiccircuit, memory element, capacitor, photovoltaic (PV) cell, chargeinjection layer, Schottky diode, planarising layer, antistatic film,conducting substrate or pattern, photoconductor, electrophotographicelement comprising one or more compounds, formulations or layersaccording to claim
 1. 21. An OFET device comprising an organicsemiconductor layer and further comprising a gate insulator layer,wherein the gate insulator layer comprises a fluoropolymer and/or thegate insulator layer is deposited from a formulation comprising aninsulator material and one or more fluorosolvents.
 22. An OFET deviceaccording to claim 21, wherein the organic semiconductor layer comprisesa formulation comprising a semiconductor compound and an organic binder.23. An OFET device according to claim 21, wherein the organicsemiconductor layer comprises a polyacene compound as semiconductingcompound.
 24. An OFET device comprising an organic semiconductor layerand further comprising a gate insulator layer, wherein the organicsemiconductor layer is as defined in claim
 15. 25. An electronic deviceor OFET device according to claim 19, which is a top gate OFET device.26. An electronic device or OFET device according to claim 19, which isa bottom gate OFET device.